The present invention relates to a passive infrared intrusion detector, and particularly to such detectors which are arranged for mounting to the ceiling of a room or other space to be protected.
U.S. Pat. No. 4,275,303, which is assigned to the same assignee as the present invention, describes a passive infrared intrusion detector which includes an enclosure having an aperture with a multi-segment Fresnel lens which is provided for focusing infrared energy onto a sensing element within the enclosure. The device described in the referenced patent, and many other prior art passive infrared intrusion detectors, are arranged for mounting to the wall of a room to be protected, so that the beams of infrared sensitivity radiate outward from the wall, often in multiple directions.
It is an object of the present invention to provide a new and improved passive infrared intrusion detector, which is is arranged for mounting to the ceiling of a room to be protected, whereby beams of infrared sensitivity can radiate in many directions and reach areas throughout the room, which might be otherwise blocked from observation by a single wall mounted detector.